The present invention generally relates to methods of using an Infrared Emission Microscope (IREM) to analyze a die and specifically backside Photon Emissions Microscopy (backside PEM). The present invention more specifically relates to a new application of using an Infrared Emission Microscope (IREM) to perform wafer-level backside analysis.
Infrared Emission Microscopes (IREMs) have been used in the semiconductor industry to locate hot carrier emission and thermal emission sites in CMOS ICs (integrated circuits). They monitor visible and near-infrared photon emissions from ICs where they are powered up or exercised, for the purpose of locating and characterizing defects. The photons emitted from transistors, pn-junctions and other photon-generating structures are collected during analysis.
There are two major types of Photon Emission Microscopy (PEM): Frontside Photon Emission Microscopy that detects photon emerging from frontside of a die, and Backside Photon Emission Microscopy that detects photons passing through the silicon substrate and emerging from the backside of a die. With the ever-increasing number and density of metal layers in today""s process technology, Frontside Photon Emission Microscopy as a fault location technique is being used less and less. Silicon allows the transmission of photons with energies less than its indirect bandgap energy (1.12 eVxe2x88x9d1.107 xcexcm wavelength for undoped silicon). By thinning heavily doped silicon substrates, and taking advantage of Silicon""s transparency to certain xcex, backside Photon Emission Microscopy is possible
At the die level, backside Photon Emission Microscopy (PEM) is a straightforward procedure of biasing the device and collecting photons. At wafer-level, this task becomes complicated because there are the various dice on the reticle field and the numerous reticle fields on the wafer, and it is difficult to tell which die is the DUT (device under test) from the backside. A new method for die location must be provided before wafer-level Backside PEM can be performed. An aspect of the present invention provides such a method.
A general object of an embodiment of the present invention is to provide a method for performing backside Photon Emission Microscopy (PEM) on wafer-level failure analysis.
Briefly, and in accordance with at least one of the foregoing objects, an embodiment of the present invention provides a method for performing backside Photon. Emission Microscopy (PEM) on wafer-level failure analysis, where the method provides that a die is located by applying reversed-biased voltage to the wafer and the backside of the wafer is observed. The die of interest will illuminate brightly, because of the electron-hole recombination from the reverse-biased protection diode. Such a method is easy to perform and provides a low cost and time-saving way to accurately identify a die and acquire emission.